Metal and semiconductor nanoparticles have shown great potential for various applications in the areas of photovoltaics, memory storage, and computing (Ref. 48). However, fine control of the nanoparticles' spatial distribution and macroscopic orientation is required to realize this potential. Indeed, to compete with preexisting technologies, this fine control must be exerted through a technique that is simple and efficient yet able to pattern the nanoparticles uniformly over large areas. Block copolymers (BCPs) have been used in attempts to achieve such control—one block can be tailored to have preferential interactions with certain nanoparticles. However, therein lies a significant problem—this method requires surface modification of the nanoparticles and specially designed polymers as well as precise control of both nanoparticle and polymer sizes and compositions. In addition, though this will cause nanoparticles to segregate to specific microdomains, there has been no success in controlling the inter-particle ordering within these microdomains—a factor critical to device performance. The ability to tailor such ordering and to arrange the particles within these microdomains via external stimuli is very desirable, but remains a significant challenge.
Facile control over the spatial distribution of nanoscopic building blocks, such as nanoparticles (NPs), from nanoscopic to macroscopic length scales, has been a major impediment in the “bottom-up” fabrication of functional materials. Precise manipulation of NP assemblies would enable one to capitalize on the plethora of available nanoparticles with unique optical, electronic or magnetic properties so as to generate functional devices, ranging from sensors and memory storage to photovoltaic, plasmonic and other microelectronic devices. Albeit challenging, additional control using external stimuli to direct the ordering and local environment of NPs, would be ideal for the design of responsive functional nanocomposites.
Various routes to direct NP assemblies have been explored, including the use of DNA and functional polymers. Programmable DNA linkers have been shown to be effective in obtaining nanoparticle arrays with tunable symmetry and dimensionality. However, large-scale fabrication poses a significant hurdle for many practical applications. Block copolymers (BCPs), on the other hand, self-assemble into well-defined arrays of nanostructures over macroscopic distances, presenting an ideal platform for directing the assembly of NPs. However, directing the NP assembly within BCP microdomains that are tens of nanometers in size and obtaining external stimuli-responsive nanocomposites still remains a challenge. BCP chains assume a stretched, random coil configuration and provide less control over the NP assembly, generally leading to a random distribution of NPs within the microdomains. Incorporating stimuli-responsiveness into a BCP without interfering with the NP assemblies can be synthetically challenging, making it non-trivial to generate responsive nanocomposites. Furthermore, using only BCPs to guide NP assemblies requires a delicate balance between the interactions of the NP-ligands and the segments of the BCPs and the entropic penalties arising from the perturbation of the BCP chain configuration. Modifying the ligands of the NPs to make them compatible with a specific BCP is possible, but usually requires synthetic procedures that are specific to each NP core and can be synthetically challenging. Perturbing the ligand shell in exchange reactions can also alter the properties of the NPs. What is needed is a mixture of block copolymer and nanoparticles with ligands where the block copolymers bind to the nanoparticles. Surprisingly, the present invention meets this and other needs.